Rotary sprinklers having water driven ball-impact type drive motors have long been known. With such sprinklers, a drive ball is located within a drive motor enclosure, itself fixedly located within a sprinkler housing, and upon the inflow of water through tangentially directed openings formed in the motor enclosure, the drive ball is rotatably displaced within the housing and, during its rotational displacement, successively impacts an impeller element formed integrally with the rotatable outlet nozzle, thereby causing rotation of the nozzle. An example of a rotary sprinkler having such a ball-impact type drive motor is disclosed, for example, in U.S. Pat. No. 2,052,673 (Stanton). In this known type of rotary sprinkler, the motor enclosure has a relatively limited axial dimension and the rotary displacement of the drive ball is within a uniquely defined ball race into which the impeller element projects. In consequence, the successive impacting of the impeller element by the ball takes place at very short intervals (each interval corresponding to the time taken for the ball to perform a complete rotational movement within the ball race). In effect, therefore, and despite the fact that the impact element is intermittently struck by the ball, the intervals between successive impacts is so small that the impact element, and in consequence the nozzle, is substantially continuously rotated.
It is known that the range of spray of such rotary sprinklers wherein the outlet nozzle is substantially continuously rotated, tends to be very limited. It is therefore known to provide rotary sprinklers with an intermittent drive wherein a relatively significant time elapses between successive rotational displacements of the nozzle. One well-known form of rotary sprinkler wherein such spaced-apart intermittent displacements of the nozzle is achieved, is the impact hammer-type rotary sprinkler. A disadvantage of such impact hammer-type sprinklers resides in the fact that they are of a relatively complicated construction and are, on the one hand, relatively expensive and, on the other hand, involving as they do a significant number of moving parts, faulty operation of the sprinkler is likely requiring periodic maintenance and servicing.
In order to achieve the desired spaced-apart intermittent displacements of the rotary sprinkler using a ball-impact type drive motor, it is necessary to ensure that the time interval between successive impacting of the impeller element of the nozzle by the ball is substantially increased. One known way of achieving such an increase in this time interval is by extending the axial extent of the motor enclosure and providing the enclosure, in addition to its base wall (in which are located one or more tangentially directed water inlets), with an outwardly tapering side wall, the impeller element being located adjacent the flared mouth of the enclosure. With a rotary sprinkler having such a drive motor (shown, for example, in U.S. Pat. Nos. RE 25942 and 2,990,120 (Reynolds), once the drive ball is set into rotational displacement under the influence of the tangentially directed water inflow, the ball effectively climbs the outwardly tapering wall of the enclosure in an upwardly directed rotary manner, and only when the ball has reached the upper end of the enclosure does it strike the impeller element rotating the latter and thereby imparting an instantaneous rotation to the nozzle. After striking the impeller element, the momentum of the ball is lost and the ball moves gravitationally downwards, only to be struck again by the tangentially directed water inflow and to repeat its rotational upward movement until it again strikes the impeller element. In this way, it is ensured that the successive impacting of the impeller element by the ball is significantly spaced apart in time.
With such known rotary sprinklers, however, the first impacting contact between the drive ball and the impeller element takes place when the upper tip of the drive ball contacts the impeller element. In view of the fact that contact between the drive ball and the impeller element is limited to the tip of the drive ball, there is not really an effective transfer of momentum of the drive ball to the impeller element, and the rotary displacement of the impeller element, and in consequence the rotary nozzle, may well prove to be inadequate.